1. Field of the Invention
The present invention relates to a zoom lens, for example, a zoom lens suitable for an optical system of an optical apparatus, such as a projection optical system of a liquid crystal projector which projects image information on a predetermined surface, and a photographing optical system of a camera.
2. Description of the Related Art
For a zoom lens of a liquid crystal projector, there are extremely strict requirements for specifications regarding color misregistration (lateral chromatic aberration) in response to a demand for higher definition. A zoom ratio of the zoom lens of the liquid crystal projector has been approximately 1.2 to 1.3, which has not been very large as compared with specifications of an interchangeable lens of a single-lens reflex camera or the like. Therefore, in designing the zoom lens for the liquid crystal projector, correction of the lateral chromatic aberration has been considered as the most important problem, and a zoom lens which has solved the problem has been proposed (see, U.S. Pat. No. 6,816,320 and U.S. Pat. No. 7,016,118).
In recent years, it has been strongly desired that the zoom lens for use in the liquid crystal projector have a higher zoom ratio, a wider angle of view, a larger aperture for using illumination light with higher efficiency, and high optical performance in an entire zoom range. Those items are largely involved in various aberrations of the zoom lens, which mainly include a spherical aberration and the lateral chromatic aberration, and with variations of the aberrations due to zooming of the zoom lens.
In particular, of those items, it has been demanded that the variations of the lateral chromatic aberration and the spherical aberration due to the zooming which largely affect the optical performance are reduced.
However, in order to obtain the high optical performance while correcting the lateral chromatic aberration and the spherical aberration over the entire zoom range, constructions and materials of the respective lenses must be set appropriately.